1. Field of the Invention
The invention relates to a cladding panel with two pairs of side edges lying opposite to one another and, in particular, a cladding panel having at least one pair of side edges provided with a coupling device embodied essentially in the form of a groove and a tongue and extending along the respective side edge.
2. Discussion of Background Information
Cladding panels of this type are generally known. Reference is made by way of example to EP 1 036 244 B1.
Generic panels are usually produced by essentially cuboid-shaped raw panels, i.e., raw panels, having side surfaces which are assigned to the side edges that run essentially orthogonally to the walking surface, being machined. This machining may be done, for example, by milling to form a coupling means on at least one pair of side edges, namely in the form of a groove in the area of one side surface and a tongue in the area of the other side surface. The purpose of this chip removal is thereby always to achieve the smoothest surfaces possible in order to slide two panels, which are connected to one another via a groove and a tongue, in the longitudinal direction of the respective side edge when laying the cladding panels.
One problem that generic cladding panels always have to deal with in practice is seasonal variations in relative humidity. In times of high relative humidity, the cladding panels expand because of swelling, whereas the cladding panels shrink during the heating period in winter because of low relative humidity. This swelling and shrinking causes the formation of cracks between panels abutting one another even if, as is customary with many types of cladding panels currently available on the market, the cladding panel's coupling mechanism is embodied with an integrated locking mechanism extendable in the longitudinal direction of the respective side edge of the cladding panel. These coupling mechanisms try to counteract the relative movement of the two panels in the direction of the panel plane, and orthogonally to the respective side edge. Cracks may also form from the effects of static and mechanical-dynamic stresses exerted on the floor, e.g., by heavy pieces of furniture or by walking on it. With rectangular cladding panels this crack formation problem occurs particularly at the short sides of the panels. The crack formation problem may also occur to a particular extent if the panels, as is customary today, are laid in a freely floating manner on the subfloor, i.e., are not connected to the subfloor by separate connecting means and are not glued to one another.
To prevent crack formation, EP 0 843 763 A1, EP 1 024 234 A1, and EP 1 026 341 A1, suggest a cladding panel which, when two panels are in a connected state, has a lower lip delimiting the groove of one panel and pressing against the tongue of the other panel with a prestressing force. This prestressing force is thereby produced by a permanent displacement of the lower lip from its resting position, when the panels are in an unconnected state. This permanent displacement causes a constant mechanical stress and a gradual fatigue of the panel material.